1. Field of the Invention
The present invention concerns a method for service provisioning to a subscriber terminal having roamed from a first communication network to a second communication network.
2. Description of the Prior Art
In recent years, communication networks have widely spread and are increasingly used by a still increasing number of subscribers to such communication networks. Examples of such communication networks are a telecommunication network for mobile communication between subscribers, such as the GSM network, GPRS network or UMTS network (3rd generation mobile telecommunication network). Data transmitted via those networks may either be circuit switched data such as (real-time) speech data or packet switched data such as image data etc. Also, such telecommunication networks may for example be those networks which are operated using the Internet Protocol (IP). Nevertheless, the expression communication network is intended to cover also a communication network such as the Internet itself.
For communication between subscribers, a subscriber's (or user's) terminal equipment accesses the network and communicates via the network with the far-end terminal of the communication partner. Nevertheless, a communication may take place also between the terminal and the network, for example upon configuring the services for communication for a respective subscriber's terminal. As terminals to be operated in conjunction with the communication network, for example mobile terminals communicating via a radio interface with the network may be used. Mobile terminals may be a mobile stations MS in a GSM network, a user equipment UE in UMTS networks (or UMTS_MS, shortly UMS) etc. However, also non-mobile terminals (not communicating via a radio interface) may be used for communication with/via the network such as personal computers and or laptops which may be carried by the user to another place within the network and are then again connected to the network (in this sense, also e.g. laptops could be considered as being “mobile”).
Subsequently, without the intention of any limitation of the present specification, but solely for the purpose of facilitating the description, reference is made to a communication network conforming to the standard of the 3rd generation (3G, UMTS) and which enables telephony based on the Internet Protocol (IPT: IP Telephony) (also known as “voice over IP”, “VoIP”). This example network is also referred to as 3G IPT network.
With the spreading of plural networks each operated by a different operator, it is desirable that a subscriber may be offered the services desired even if the subscriber presently communicates via a network the subscriber initially did not subscribe to. That is, normally, a subscriber subscribes to a network of a network operator and is registered to this network as the home network (also referred to as a first network in this specification). If the subscriber moves/registers to another network (visited network) to which the subscriber did not initially subscribe to (also referred to as a second network in this specification), the subscriber nevertheless desires to have communication services available.
In 3G IPT communication networks, a functional entity known as call state control function (CSCF) is adapted to provide the services to a respective terminal equipment. This entity is herein below also referred to as communication control entity. Thus, upon registration/attachment to a network (home or visited network), it is necessary that the terminal equipment discovers a call state control functional entity within the network. A network may contain several communication control entities, a respective entity being adapted for the provision of specific services not offered by the others, or each communication control entity offers the same services but serves a different network area.
For such a discovery of a communication control entity, the terminal equipment first performs an attachment to an access network (for example, GPRS network, General Packet Radio Service) as a part of the communication network. In order to be provided with Internet Telephony service (IPT services) the terminal equipment has to perform a CSCF discovery procedure in order to get an address of the communication control entity (CSCF), that is in order to “learn”, where the communication control entity is located in the network such that it can be contacted for service provisioning.
Recently proposed CSCF discovery methods, however, are not yet fully satisfactory. Namely, those CSCF discovery methods are either suitable for discovering the communication control entity of the home network or for discovering the communication control entity of the visited network. The subscriber can get services either from home NW or visited NW but not from both at the same time.
However, both of the above mentioned concepts have some limitations and difficulties. In particular, in a case when only the visited NW provides the services, it may offer different services as compared to the home network of the subscriber, then limitations as to the available services may be imposed on the subscriber. This means, that the subscriber may for example be impeded to use services offered by the subscriber home network, but which are not implemented in the visited network. In the opposite case, when only the Home NW provides services, there are difficulties with providing location-dependent services like for example the “Order the Pizza” one.
Consequently, the subscriber does not have the combined benefit of the services offered by both the home network and the visited network, since the existing scenarios do not support flexibility of service discovery (CSCF discovery) for a roaming subscriber.